In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
With the purpose of increasing the stability in milling, in particular face or end milling, of materials, such as titanium, steel, aluminium or castings, it is previously known to place the milling inserts that are in the same radial plane, for example, in the same horizontal plane if the rotation axis of the milling cutter body is vertical, with different or irregular angles between two adjacent milling inserts, for example, that there is around the circumference of the milling cutter body different or irregular distances in the rotational or peripheral direction between two adjacent milling inserts. This angular displacement of the milling inserts or uneven pitch of the milling inserts is denominated differential pitch. Differential pitch means that the engagement frequency of the milling inserts can be varied and the risk of self oscillations and instability can be reduced and an increased critical cutting engagement is obtained.
U.S. Pat. No. 5,876,155 discloses a method for plunge-cut milling wherein three milling inserts are situated at somewhat different radial distances from the rotation axis and wherein the milling inserts are intended to machine three different surfaces in the workpiece situated at different depths and having different angles. It is shown that the three milling inserts can be placed with differential pitch.
EP-B1-1 276 580 discloses a milling tool wherein a milling insert in a radial series of three milling inserts is situated at a greater radial distance from the rotation axis of the milling cutter body in relation to the two other milling inserts of the same radial series. By series, radial series, or radial set, it is meant that those milling inserts are essentially in the same radial plane, with the radial plane being perpendicular to the rotation axis of the milling tool.
U.S. Pat. No. 7,399,146 discloses a milling tool with differential pitch wherein a milling insert is angularly displaced in relation to the other two milling inserts of the same series, whereby different angles between the milling inserts are established.
WO-A1-2005/058534 discloses a milling tool having overlapping planes wherein a first milling insert in a chute has another length than the other milling inserts in the same chute.
US-A1-2004/0170480 and WO-A2-2007/077535 disclose end milling cutters or shank-end mills having different axial clearance angles and radial clearance angles, respectively, of the peripheral cutting edges of the respective end milling cutter.